Lamp units developed to illuminate a space, surface or an object use different materials, designs and are applicable for multiple lighting purposes. The majority of such lamp units are now generally known to employ Light Emitting Diode (“LED”) technology as a replacement for conventional incandescent and/or fluorescent lighting to provide a lighting source that generates white light having a relatively high Colour Rendering Index (“CRI”), so that spaces, surfaces, and objects illuminated by the lighting appear as if illuminated by natural sunlight. The ability of a light source to render the color of an object is measured using the CRI which provides a measure of how a light source makes the color of an object appear to the human eye and how well subtle variations in color shade are revealed. In applications where accurate color rendition is required, such as for example retail lighting, museum lighting and lighting of artwork, a high CRI typically of at least 80 is highly desirable.
Lighting technologies that are currently available on the market (e.g. halogen or fluorescent) have unstable spectral outputs which shift over their lifetimes due to high operating temperatures tending to degenerate the chemicals employed to emit light, thus reducing the CRI for these light sources. As a consequence, white LEDs are increasingly being used to replace conventional fluorescent, compact fluorescent and incandescent light sources due to their long operating life expectancy and high luminous efficacy. However, one of the drawbacks associated with white LEDs is related to their spectrum output which have undesirable light wavelengths such as the ultraviolet (“UV”) and Infrared (“IR”) wavelengths. The use of filters to eliminate these undesirable UV and IR wavelengths allow the visible light to pass while decreasing the intensity of the unwanted wavelengths. However, employing filters also significantly decreases the intensity of the visible light and still UV and IR wavelengths may not be fully attenuated.
Yet another drawback of white LEDs relates to spikes in the light spectrum caused by white LEDs which reduces the CRI quality. For example, U.S. Pat. No. 8,592,748 B2, issued to Gall et al., entitled “Method and arrangement for simulation of high-quality daylight spectra,” discloses a method and a multispectral color coordination system that simulates high-quality daylight spectra using LEDs disposed in groups with each group emitting light at different wavelengths within the daylight spectrum. The wavelength of the light emitted by the white LED creates a spike in the spectral power distribution curve which contains a large portion of yellow-green to yellow light in a spectral range of 555 to 590 nm not representative of natural lighting.
While Red-Blue-Green (“RGB”) coloured LED combinations may be employed to produce white light without employing white LEDs, such a combination of LEDs however do not provide a uniform spectral progression between the wavelengths ranging between from 380 nm to 780 nm to properly simulate natural light. Since colored light emitting diodes produce light only at specific wavelengths with the spectral power distributions of the component LEDs being relatively narrow, perceivable color shift occurs.
Therefore, what is needed is a system and method for creating natural day-light spectra with High-CRI or High-Color Quality Scale (“CQS”) without the use of white LEDs and without undesirable UV and IR wavelengths.